THE PROPERTIES

46

pounders, should be rammed in proportion to the weight ofthe charge, in order to produce the proper effect ; perhapstoo much force cannot be used, provided that the grains ofpowder are not crushed and beat so close as to prevent thefire from penetrating. The charge for richochet and red-hot firing, is very small in proportion to the calibre; it de-pends in sieges on the situation of the gun, as the distancefrom the enemies batteries is the only point to be considered.The charges for field artillery in general actions, in affairsof posts, in attack and defence of intrenchments, &c. shouldbe between 4 and 4 of the weight of the shot, according tothe calibre and weight of the gun.

no. Though our observations have been hitherto confinedto the proper charges for guns; yet those for mortars may beeasily ascertained by knowing the quality of the powder, andthe form of the chamber. All the mortars now in use, inwhich the communication between the chamber and thechase is narrower than the greatest diameter of the chamber,as the spherical, elliptical, parabolic, and those in form of apear, always range the farthest, when the chambers are filledwith the common cannon powder, and the shell closely con-fined by well sifted earth rammed upon it; it is clear in thiscafe that the charge cannot be augmented. Beside the con-cussion is more violent, and the ranges are less exact, whenthe chambers are not filled; therefore, to throw a shell to acertain point, the chamber should be filled, and the rangeregulated by the degree of elevation,

in. We will conclude this chapter by shewing experimen-tally how much the difference in the size of the vent affects theforce of the shot. A musquet was taken -■& of an inch indiameter, and 33 inches in length of barrel. The axis ofthe large screw which closes the breech, was perforated witha hole of in inch in diameter, with spiral sides to receive asmaller screw; one end of the smaller screw was armed with alittle piece of red hot iron, to set fire to the powder in thebarrel; to the other end a winch was fixed to screw it up;at the part where the vent is generally placed, a circular holewith spiral sides was drilled -rs of an inch in diameter, towhich three fcrfews were successively applied ; the first exactlyclosed the opening, and consequently forced all the firedpowder to pass through the muzzle. The second had in itsaxis a hole or vent ^ of an inch in diameter, through which apart of the fluid might escape; and the third had a vent of T %-